The invention relates generally to diagnostic imaging and, more particularly, to a multiple x-ray tube system and method of making same.
X-ray systems typically include an x-ray tube, a detector, and a support structure for the x-ray tube and the detector. In operation, an imaging table, on which an object is positioned, is located between the x-ray tube and the detector. The x-ray tube typically emits radiation, such as x-rays, toward the object. The radiation typically passes through the object on the imaging table and impinges on the detector. As radiation passes through the object, internal structures of the object cause spatial variances in the radiation received at the detector. The detector then emits data received, and the system translates the radiation variances into an image, which may be used to evaluate the internal structure of the object. One skilled in the art will recognize that the object may include, but is not limited to, a patient in a medical imaging procedure and an inanimate object as in, for instance, a package in an x-ray scanner or computed tomography (CT) package scanner.
Some applications for x-ray imaging using x-ray tubes include dual kVp operation to enable energy discrimination by using detectors configured to be responsive to different x-ray spectra. For example, a conventional third-generation CT system may acquire x-ray projection data sequentially at different peak kilovoltage (kVp) levels of the x-ray source, which changes the peak and spectrum of energy of the incident photons comprising the emitted x-ray beams. Energy sensitive detectors may be used such that each x-ray photon reaching the detector is recorded with its photon energy. The detected signals from two energy regions provide sufficient information to resolve the energy dependence of the material being imaged. Furthermore, detected signals from the two energy regions provide sufficient information to determine the relative composition of an object composed of two hypothetical materials.
It is generally desirable to have increased speed, coverage, and resolution of CT scanners, for example, to improve imaging of the cardiac region. In recent years, manufacturers have improved scanners by increasing the gantry speed, by reducing the pixel size, and by extending the coverage of the detectors in a z-direction (e.g., axial or along the patient axis of a CT system) by extending the length of the detector in the z-direction. This approach has resulted in development of CT systems that have larger detectors. Detectors, in principle, may be extended in the z-direction to cover the entire cardiac region. However, such a length may be undesirable because, as detectors get longer in the axial (z) direction, an increase in the cone angle occurs as well. The cone angle is the angle, along the z-direction, between the focal spot and the edges of the detector. At small cone angles (i.e., at the center region of the cone), complete data sets are obtained. However, data is incomplete at increased cone angles (i.e., at the outer edges of the cone), which results in unstable reconstruction and leads to cone beam artifacts in reconstructed images.
Cone beam angles may be decreased by emitting x-ray beams from multiple x-ray tubes that are spaced apart from one another along the z-direction. However, properly aligning and calibrating the x-ray tubes along the z-direction adds significant complexity to the manufacturing process and, therefore, increases the cost of the imaging system.
Therefore, it would be desirable to design a system and method that reduces cone beam artifacts while simplifying the manufacturing complexity of the imaging system.